When fossil fuels are burned, the resulting flue gases often contain pollutants that include oxides of sulfur (e.g., SO.sub.2) and oxides of nitrogen (e.g., NO). When metal ores are subjected to oxidation, such as during metal-winning operations, polluting gaseous oxides of sulfur and nitrogen are also produced. When waste materials are incinerated, the flue gases can contain not only oxides of sulfur and nitrogen but also gaseous chlorinated compounds such as HCl. Such acidic gaseous products are serious air pollutants and are also corrosive. Thus it is common practice to remove such acidic polluting gases from flue gases before they are discharged to the atmosphere. Removal of acidic gases such as NO.sub.x, SO.sub.x or HCl is often accomplished by contacting the flue gas with alkaline earth compounds. As explained hereinbelow, the utilization of such compounds for capture of acidic gases from flue gases is generally in need of improvement regarding achieving more thorough utilization of the total capacity for chemical reaction of these compounds with acidic polluting gases. Moreover, it would be preferable to use or re-use waste materials for such purposes instead of virgin materials or primary or intentionally manufactured substances.
Illustrative procedures for removing acidic pollutants from flue gas are disclosed in a number of U.S. patents and all U. S. patents cited anywhere herein are intended to be fully incorporated herein by reference. In U.S. Pat. No. 4,246,245 dated Jan. 30, 1981, Abrams et al. remove SO.sub.2 from gases containing the same. in either a wet or dry scrubbing process by contacting the gas with a Type S hydrated lime, which is a calcined dolomite hydrated in an autoclave at pressures of about 25 to 100 psi and temperatures of about 250.degree. F. to 400.degree. F. In U.S. Pat. No. 4,409,192 dated Oct. 11, 1983, Lichtner et al. remove SO.sub.2 from flue gas by contacting the gas with an aqueous medium containing a water-soluble sulfonated polystyrene, an organophosphonate and a material which will react with SO.sub.2 to form calcium sulfate or calcium sulfite and then separating the resulting insoluble calcium compounds from the aqueous medium. Lester et al. disclose, in U.S. Pat. No. 4,423,018, dated Dec. 27, 1983, removing SO.sub.2 from a flue gas by contacting the gas with an aqueous slurry of limestone or lime buffered with a byproduct stream obtained from the manufacture of adipic acid.
College and Vlnaty disclose, in U.S. Pat. No. 4,626,418, dated Dec. 2, 1986, the removal of SO.sub.2 from a gaseous mixture containing SO.sub.2 by using a mixture containing a sugar and at least one alkaline earth compound selected from the group consisting of calcium and magnesium carbonates, oxides and hydroxides. A similar process is disclosed by Robinson in U.S. Pat. No. 4,861,568 dated Aug. 29, 1989. In U.S. Pat. No. 5,181,916 dated Feb. 16, 1993, Nevels discloses purifying flue gases of acidic polluting gas by contacting the flue gases with residual liquids originating from photographic, photochemical and galvanic industries. Moran et al., in U.S. Pat. No. 5,223,239 dated Jun. 29, 1993, teach a method of preparing hydrated lime for use as a sorbent for SO.sub.2 removal from gas streams in which an aqueous solution of an organic solvent is used to hydrate the lime and to wash the resulting hydrate prior to drying it.
Sugar is manufactured by extracting it from plant material (e.g. sugar beets or sugar cane) into aqueous solution. The aqueous extraction produces a solution (sometimes called juice) containing, in addition to sugar, many impurities that usually are subsequently removed by adding milk of lime (a aqueous suspension of lime) and heating to about 90.degree. C. in purification steps. In the purification process, calcined limestone (CaO) is mixed with water to produce a milk of lime slurry that is added to the beet juice in two doses called "pre liming" and "liming". Neutralization of acidity and coagulation/precipitation of proteins is associated with "pre- liming" whereas reactive destruction of impurities such as invert sugars is associated with liming. Carbonation steps (by bubbling CO.sub.2) usually follow the liming steps; during carbonation, excess alkalinity is removed and calcium carbonate is precipitated. This precipitate is believed to cause further purification of the juice by sorption and occlusion of impurities on the fine CaCO.sub.3 particles that are co-precipitated and thereafter readily filtered. Sometimes the precipitated CaCO.sub.3 is referred to as a filter aid as well as a reagent for chemical purification of the sugar juice. The quantities of CaO added are about 2-3% by weight of the juice.
During liming, the addition of milk of lime causes coagulation and precipitation of impurities and this use of lime is often referred to as defecation. The juice is usually held at an elevated temperature during defecation. During defecation, a considerable excess of lime is introduced and this excess is subsequently precipitated as calcium carbonate by contacting the mixture with CO.sub.2 during a carbonation step. The fine crystalline precipitate of CaCO.sub.3 produced by carbonation causes additional purification of the sugar solution; this additional purification results from adsorption or occlusion of non-sugars by the precipitated particles of CaCO.sub.2. Separation of solid material (e.g., by filtration) from the defecated and carbonated juice produces a filtered sugar juice and a solid material (solid residue) containing substantially all solid impurities and precipitated CaCO.sub.3 ; MgCO.sub.3 can also be present in this solid waste residue in the event the original lime employed was prepared from a dolomitic limestone containing Mg in addition to calcium. The clarified juice from a first liming, carbonation and solid separation is often treated by a second sequence of liming, carbonation and separation (e.g., filtration), thereby producing additional solid residue.
The solid material removed from the purified juice (e.g., by filtration) is a waste residue material that is a byproduct of sugar refining and is often referred to as filter-press mud. Herein this solid waste byproduct material is often referred to by the acronym SRSR that stands for solid residue from sugar refining. The SRSR is sometimes rinsed with water to remove residual sugar and it is then usually de-watered in a de-watering pond or lagoon or a de-watering stockpile. Although the SRSR can contain up to about 2% sugar as it comes from the separation step (e.g., filtration), during the slow, subsequent de-watering process residual sugar is essentially completely removed by a combination of rainwater leaching and microbial action, sugar-consuming microbes being natural inhabitants of the original plant material of the sugar beets or sugar cane. These microorganisms are naturally present in the original raw material and persist throughout the various process steps. Such sugar-consuming micro-organisms are generally present in very large population densities within biofilm that forms on and adheres to particles of SRSR byproduct that are filtered from the juice. General background material on the formation and characteristics of such naturally occurring biofilms can be found in articles by Costerton et al. in Annual Reviews of Microbiology, vol. 49, pp. 711-745 (1995) and in Journal of Bacteriology, vol. 176, No. 8, pp. 2137-2142 (1994).
Silen (P. M. Silen, "Technology of Sugar Beet Production and Refining", OTS 63-11073, available from the Office of Technical Services, U. S. Department of Commerce, Copyright 1964, Israel Program for Scientific Translations, Inc.) gives the following typical component assay (in % of dry solids) of a filter press mud as obtained in a sugar plant while the solid mud residue still contains residual sugar (i.e. before removal of sugar by washing, by microbial action and other processes during de-watering: calcium carbonate 74.2, nitrogen-free organic compounds, nitrogenous organ compounds 5.9, sucrose 2.0, pectic substances 1.7, lime in the form of various salts 2.8, other mineral substances (including phosphoric acid) 3.9; total=100%. Further details regarding the refining of sugar solutions (juice) and regarding waste SRSR byproducts arising from such refining processes are disclosed and taught by Herzog in U.S. Pat. No. 5,191,723, issued Mar. 9, 1993, Haley in U.S. Pat. No. 3,734,773 issued May 22, 1973, Toth et al. in U.S. Pat. No. 4,795,494 issued Jan. 3, 1989 and Schoenrock et al. in U.S. Pat. Nos. 4,045,242, 3,982,956, 3,973,986 and 3,887,391 which were published on the following respective dates: Aug. 30, 1977, Sep. 28, 1976, Aug. 10, 1976, Jun. 3, 1975.
Generally, in comparison to natural limestones, waste SRSR separated (e.g., by filtration) from juice in sugar refining processes would not be expected to be a good sorbent material for acidic gases such as SO.sub.2 for the following reasons: (1) the CaCO.sub.3 or MgCO.sub.3 content of such waste SRSR byproduct is significantly lower than in limestone; (2) considerable impurities have been occluded or sorbed by precipitated particles of CaCO.sub.3 or MgCO.sub.3 in SRSR and sorbed and occluded impurities would be expected to block the surface of the particles and impede transport of acidic gas (e.g. HCl, SO.sub.x or NO.sub.x) to the surface of such particles of carbonates of alkaline earth metals in SRSR; (3) the separated waste SRSR contains adventitious solid materials brought into the sugar juice extraction process by the raw botanical plant material (e.g., sand, soil, plant fiber, leaves, etc.), all of which components further reduce the calcium content of the SRSR.
The CaCO.sub.3 -containing solid SRSR byproduct filtered from sugar juice during sugar refining processes is generally considered a waste material and it often is stockpiled on land surrounding sugar refining plants. There is a great need to find new uses for this waste material because it can cause stream pollution by siltation or leaching by rainwater and air pollution when it becomes airborne driven by winds. Furthermore, its stockpiling on land sites prevents the land from being used for other purposes (e.g., agriculture or forestry).
In addition to the Silen reference super, other general references on refining sugar and purification of sugar juices are: "Beet Sugar Technology", R. A. McGinnis, editor, 1982 and Kirk Othmer Enclyclopedia of Chemical Technology vol. 21, pp. 903-920 (1978).